This application claims the priority of German application 100 39 792.1, filed Aug. 16, 2000, the disclosures of which is expressly incorporated by reference herein.
The present invention relates to a steering column for a motor vehicle.
In the event of an impact that follows a primary collision and in which a vehicle, for example, strikes another vehicle or another obstruction, the body of a vehicle driver may, without the protection of an airbag for example, strike a steering wheel, because the airbag had deployed after the primary collision and has now collapsed again.
In order to relieve or reduce the impact acting upon the body of the driver in a secondary collision and to prevent a substantial injury to the vehicle driver by the steering column, various driver protection devices are known from the prior art and are referred to as impact-absorbing steering devices.
Thus, German Patent Document DE 195 15 009 Al proposes an impact-absorbing steering apparatus in which, by a reduction of a peak load in an initial movement of a secondary impact, impact energy caused by the secondary collision is absorbed by the flexion of a bending zone of an energy-absorbing panel. This energy-absorbing panel possesses a rear end which is retained by a vehicle body. A slot is formed in the bending region and a cross-sectional surface region is reduced so that the flexible region is easily capable of plastic deformation and can thus absorb energy.
By means of such an energy absorption panel, an increase in the peak load during the initial movement of the secondary impact is prevented despite the hardening of the bending region during the production process.
However, the type of energy absorption panels as described in that printed publication exhibit the disadvantage that they customarily require a great deal of structural space. Moreover, with such a configuration, the steering column is not guided in the event of an accident, and therefore the steering column can be displaced and deformed in an uncontrolled manner. This also can result in injury to the vehicle occupants.
German published Patent Application DE 196 21 183 discloses a telescopic column which is used for vehicles to reduce the risk of personal injury in the event of accidents. The telescopic column for vehicles described in this document, having a lower part that is disposed in an upper part in an axial telescopic manner and having a securing system for the steering column upper part, is characterized in that the securing system contains at least one component which can deform progressively in the event of an axial telescopic movement of the steering column upper part and energy absorption.
In such a telescopic column, however, the measures for energy absorption during compression of the steering column in the event of a collision have to be provided at the cost of a relatively high additional construction effort.
U.S. Pat. No. 5,961,146 discloses another energy absorbing steering column. In this case, the apparatus provided for the purpose has a first bracket, which is fixed to the steering column in a central region, and a second bracket, which is secured on the bodywork in order to support the first bracket. A connecting device that comprises an energy absorption member to assist the first bracket up to a predetermined force is additionally provided. As a result, a collision force that is applied to the steering column can be absorbed, and the first bracket is enabled to move relative to the second bracket, in order to absorb the impact energy if a particular load is applied to the steering column.
The energy-absorbing member includes a metallic wire which has a basic portion and elongated deformable portions extending respectively from the ends of said basic portion towards the free ends. Each of the deformable portions has folded-back portions and deformable portions extending from the folded-back portions towards end portions. The energy-absorbing member is retained at a basic portion of the first or the second bracket and engaged or engageable with the other bracket at its folded-back portion. When the force applied in a secondary collision exceeds a predetermined value and the first bracket moves forward relative to the second bracket, the metallic wire is pressed by the first bracket onto the folded-back portions against the bolt in order to press the folded-back portions along the deformable portions towards the free portions, thereby absorbing secondary collision energy.
In addition, German Patent Document DE 198 19 713 discloses a steering column for a motor vehicle having a steering column rotatably mounted in a tubular jacket, the tubular jacket being assigned at least one deformation element which is plastically deformable, with absorption of energy, in the event of an axial displacement of the tubular jacket. In this arrangement, the at least one deformation element is fixed to the tubular jacket on at least one side and lies on deflection means disposed fixedly on the bodywork and axially positioned, relative to the deformation element, in a manner such that the deformation element is deformed with the aid of the deflection means in the event of an axial displacement of the tubular jacket.
In these two previously described steering columns, however, it has proved to be a disadvantage that the design of the arrangements for energy absorption requires a very substantial construction effort.
A further energy-absorbing steering column for motor vehicles is disclosed in German Published Patent Application DE 197 10 725 (corresponding U.S. Pat. No. 5,706,704). In this steering column described therein an energy absorber is provided having a yoke, which can pivot about a transverse center line of a vehicle body, and an energy absorption member between the yoke and the column jacket, which responds to a linear movement of the column jacket relative to the yoke. The column jacket extends through a drilled hole in the yoke, and a plastics bushing in the drilled hole prevents the column jacket canting relative to the yoke before and during a linear movement of the column jacket. The energy absorption member comprises a flat metallic strip that is attached to one end of the column jacket and is bent over a convex anvil on the yoke. The metallic strip is drawn over the anvil parallel to a longitudinal median line of the column jacket and is plastically deformed in order to convert into work a fraction of the kinetic energy acting on the steering column in the event of an impact.
This energy-absorbing steering column has, like the others described above, proved not very advantageous because of its very elaborate structural design.
On the above basis, it is an object of the present invention to provide a steering column for a motor vehicle by means of which, with only a slight additional construction effort, good energy absorption can be ensured in the event of an accident, in particular a second collision.
This object is achieved by a steering column for a motor vehicle having a steering shaft rotatably mounted in a tubular jacket, wherein the tubular jacket is secured in use at a vehicle bodywork end on two rails extending substantially in an axial direction, the tubular jacket being guided between the rails in the event of an axial displacement, wherein at least one rail is provided with at least one deformation element plastically deformable and secured at least at one end on the respective at least one rail, with absorption of energy, in the event of an axial displacement of the tubular jacket in case of a crash in a manner such that the respective at least one deformation element is deformed by rolling friction via deflector structure fixedly disposed on the tubular jacket.
As a result of the design, according to the invention, of the steering column comprising a steering shaft and a tubular jacket, which is secured on two rails fixed to the bodywork and can be guided between these rails in the event of an axial displacement, at least one rail being assigned a deformation element which is plastically deformable with energy absorption in the event of an axial displacement of the tubular jacket in case of a crash, it is first possible for the structural space for the steering column to be very small, and in particular very shallow, and in addition for sufficient energy absorption by rolling friction to be ensured in the event of an axial displacement. The tubular jacket being guided, in case of a crash, by the rails extending substantially in the axial direction, the tubular jacket being moved forward in a guided manner and not arbitrarily moved into the engine compartment and deformed.
In order not only to provide for energy to be absorbed by the deforming of the deformation element but also to achieve a movement in the forward direction of travel by the releasing of the tubular jacket from the rails, the tubular jacket in certain preferred embodiments is secured on the rails via plastic shearing pins which can be released above a certain axial force and hence also absorb energy.
As a result of the fact that such rails are frequently also provided with slots, which likewise extend in the axial direction, and customarily serve for the longitudinal adjustment of the steering column, a telescopic steering column having deformation elements can be provided without any additional structural space requirement.
According to one embodiment, the deformation element is formed as a sheet metal strip. This sheet metal strip is guided around deflection means, such as, for example, bolts and/or housing edges. The radii or the reciprocal distances apart for the deflection means may be variable and may be selectively set. As a result, the degree of reshaping of the sheet metal strip can be varied and the level of the energy to be absorbed thus set. This entails the advantage that widely differing requirements, such as for example different country-specific requirements, can be met with one and the same apparatus. It is also contemplated by certain embodiments of the invention to make the adjustment dependent on the specific crash conditions and to perform the setting only shortly before an impact.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.